Electronic brake system

ABSTRACT

An electronic brake system may be capable of performing braking operation according to a pedal effort of a driver even when the brake system operates abnormally as well as simplifying a configuration thereof by minimizing the number of valves for controlling a flow of oil pressure and precisely controlling pressure therein.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Korean Patent Application No.2014-0193773, filed on Dec. 30, 2014 in the Korean Intellectual PropertyOffice, the disclosure of which is incorporated herein by reference.

BACKGROUND

1. Field

Embodiments of the present invention relate to an electronic brakesystem, and more particularly, to an electronic brake system capable ofa structure simplification and a precise pressure control.

2. Description of the Related Art

Every vehicle requires a braking ability and thus requires a brakesystem, and recently, various types of the brake systems have beenproposed for realizing stronger and more stable braking forces. Examplesof the brake systems include an anti-lock brake system (ABS) whichprevents wheel slip during braking, a brake traction control system(BTCS) which prevents driving wheel slip when a sudden acceleration or arapid acceleration occurs in a vehicle, and an electronic stabilitycontrol system (ESC) which together with the ABS and BTSC to control ahydraulic pressure of a braking system so that a vehicle is maintainedunder a stable driving condition, etc.

Such an electronic brake system includes a plurality of solenoid valvesfor controlling a brake oil pressure transferred to wheel cylinders(referred to as hydraulic brakes or disk brakes) mounted on the wheelsof a vehicle, a pair of low pressure accumulators for temporarilystoring oil discharged from the wheel cylinders, a motor and a pump forforcibly pumping the oil stored in the low pressure accumulators, aplurality of check valves to prevent a backflow of oil, and anelectronic control unit (ECU) for controlling the operations of thesolenoid valves and the motor which are compactly built in an oilpressure block formed of aluminum. Further, a hydraulic pressure supplyunit is provided and being used, that receives an electrical signal froma pedal displacement sensor for detecting a displacement of the brakepedal responding to the driver's intention to brake when a driver stepson a brake and supplies pressure to the wheel cylinders.

The electronic brake system provided with the above hydraulic pressuresupply unit is disclosed as European Patent No. 2520473. According tothe disclosure, the hydraulic pressure supply unit is designed togenerate a brake pressure by operating a motor according to a pressureon the brake pedal. Here, the brake pressure is generated by convertinga rotatory power of the motor to a rectilinear movement to press apiston.

However, in the electronic brake system with the above structure, thearrangement of the plurality of solenoid valves provided to control thepressure transferred to the wheel cylinders is complex, and, inaddition, the plurality of solenoid valves are individually operated tocontrol a hydraulic pressure delivered to the wheel cylinder provided ineach wheel, thereby increasing the vibration and the noise due tooperating the solenoid valves.

Further, since the configuration of the plurality of the solenoid valvesand the flow paths for controlling the pressure according to variouscontrol modes becomes complex and in addition, the weight and the volumeof the system are increased because a motor, a pump, and a low pressureaccumulator are provided additionally, the ease of mounting and theefficient use of space are compromised, and vibration and noise due tomotor and pump operations are increased.

SUMMARY

Therefore, it is an aspect of the present invention to provide anelectronic brake system capable of performing braking according to apedal effort of a driver even when a brake system operates abnormally aswell as simplifying a configuration thereof by minimizing the number ofvalves for controlling a flow of oil pressure and precisely controllingpressure therein.

Additional aspects of the invention will be set forth in part in thedescription which follows and, in part, will be obvious from thedescription, or may be learned by practice of the invention.

In accordance with one aspect of the present invention, an electronicbrake system includes a reservoir in which oil is stored, a mastercylinder having a first oil pressure port and a second oil pressure portand coupled with the reservoir to receive the oil, a pedal displacementsensor configured to detect a displacement of a brake pedal, and asimulation device connected to the master cylinder and provided so thatreaction is provided according to a pedal effort of the brake pedal, andthe electronic brake system includes a hydraulic pressure supply unitconfigured to output an electrical signal through the pedal displacementsensor to operate a motor when the brake pedal operates, and configuredto convert rotatory power of the motor to rectilinear movement, an oilpressure control unit having a first oil pressure circuit and a secondoil pressure circuit connected to the hydraulic pressure supply unitthrough a main oil pressure path, and each configured to control twowheels so that a hydraulic pressure is received using a force generatedby the hydraulic pressure supply unit to perform braking, and anelectronic control unit configured to control the motor and valves basedon hydraulic pressure information and pedal displacement information,wherein the oil pressure control unit includes a first inlet valve and asecond inlet valve respectively disposed at upper streams of two wheelcylinders to control the hydraulic pressure flowing into the two wheelcylinders respectively installed on the two wheels provided in the firstoil pressure circuit, a third inlet valve and a fourth inlet valverespectively disposed at upper streams of two wheel cylinders to controlthe hydraulic pressure flowing into the two wheel cylinders respectivelyinstalled on the two wheels provided in the second oil pressure circuit,a first balance valve configured to connect or disconnect the two wheelcylinders to which the first inlet valve and the second inlet valve areconnected, and a second balance valve configured to connect ordisconnect the two wheel cylinders to which the third inlet valve andthe fourth inlet valve are connected, wherein the hydraulic pressuredischarged from the four wheel cylinders is controlled by a rotation ina direction opposite a rotation direction of the motor of the hydraulicpressure supply unit while braking.

The inlet valves may be provided with solenoid valves in a normal closedtype which operates a valve to be open when an open signal is receivedin a state in which the valve is closed at ordinary time.

When the hydraulic pressure is discharged from the wheel cylinders byrotating the motor of the hydraulic pressure supply unit in a reversedirection, the first inlet valve and the second inlet valve may be open.

When the hydraulic pressure is discharged from the wheel cylinders byrotating the motor of the hydraulic pressure supply unit in a reversedirection, only one of the first inlet valve and the second inlet valvemay be open and only one of the third inlet valve and the fourth inletvalve may be open.

The first and second balance valves may be provided with solenoid valvesin a normal open type which operates a valve to be closed when a closesignal is received from the electronic control unit in a state in whichthe valve is open at ordinary time.

The electronic brake system may further include a first backup pathconfigured to connect the first oil pressure port and the first balancevalve so that oil is directly supplied to the wheel cylinders when theelectronic brake system operates abnormally, a second backup pathconfigured to connect the second oil pressure port and the secondbalance valve, a first cut valve provided on the first backup path andconfigured to control a flow of the oil, and a second cut valve providedon the second backup path and configured to control a flow of the oil.

The first and second cut valves may be provided with solenoid valves ina normal open type which operates a valve to be closed when a closesignal is received from the electronic control unit in a state in whichthe valve is open at ordinary time.

The hydraulic pressure supply unit may include a motor configured togenerate a rotatory power by the electrical signal of the pedaldisplacement sensor, a power converter configured to convert a rotarymovement of the motor to a rectilinear movement, an oil pressure pistonconnected to the power converter and configured to perform a rectilinearmovement, a pressure chamber slidably provided with the oil pressurepiston and connected to the first and second oil pressure circuitsthrough the main oil pressure path, and an oil pressure spring providedin the pressure chamber and configured to elastically support the oilpressure piston, wherein the pressure chamber may be connected to thereservoir through an oil path to receive the oil.

A check valve may be installed on the oil path to prevent a flow of apressure of the pressure chamber backward, and to suction and store theoil in the pressure chamber when the oil pressure piston is returned.

BRIEF DESCRIPTION OF THE DRAWINGS

Hereinafter, while the present invention will be described in detailwith reference to the accompanying drawings, since following drawingsdeal with exemplary embodiments of the present invention, the spirit andscope of the present invention should not be limited to the followingdrawings:

FIG. 1 is an oil pressure circuit diagram illustrating an un-brakedstate of an electronic brake system according to one exemplaryembodiment of the present invention;

FIG. 2 is an oil pressure circuit diagram when a brake of an electronicbrake system operates normally according to one exemplary embodiment ofthe present invention;

FIG. 3 is an oil pressure circuit diagram when a brake of an electronicbrake system is released normally according to one exemplary embodimentof the present invention;

FIG. 4 is an oil pressure circuit diagram for describing an anti-lockbrake system (ABS) being operated by an electronic brake systemaccording to one exemplary embodiment of the present invention;

FIG. 5 is an oil pressure circuit diagram for describing an electronicbrake system being operated in a dump mode, according to one exemplaryembodiment of the present invention; and

FIG. 6 is an oil pressure circuit diagram when an electronic brakesystem operates abnormally, according to one exemplary embodiment of thepresent invention.

DETAILED DESCRIPTIONS

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings. The embodiments areprovided in order to fully explain the spirit and scope of the presentinvention for those skilled in the art. Thus, the present inventionshould not be construed as limited to the embodiments set forth hereinand may be accomplished in other various embodiments. Parts irrelevantto description are omitted in the drawings in order to clearly explainthe present invention. The sizes of the elements in the drawings may beexaggerated in order to facilitate understanding.

FIG. 1 is an oil pressure circuit diagram illustrating an un-brakedstate of an electronic brake system according to one exemplaryembodiment of the present invention.

Referring to the drawing, the electronic brake system generally includesa master cylinder 20 which generates a hydraulic pressure, a reservoir30 coupled with an upper portion of the master cylinder 20 to store oil,an input rod 12 which presses the master cylinder 20 according to apedal effort of a brake pedal 10, a wheel cylinder 40 to which thehydraulic pressure is transferred to perform a braking action of eachwheel RR, RL, FR, and FL, a pedal displacement sensor 11 which detects adisplacement of the brake pedal 10, and a simulation device 50 whichprovides a reaction against the pedal effort of the brake pedal 10.

Here, the master cylinder 20 is formed with at least one chamber togenerate the hydraulic pressure. According to the drawing, a firstpiston 21 a and a second piston 22 a form two chambers, and the firstpiston 21 a is in contact with the input rod 12. In order to ensuresafety in a breakdown, the master cylinder 20 has two chambers. Forexample, one of the two chambers is connected to a right front wheel FRand a left rear wheel RL of a vehicle, and the other chamber isconnected to a left front wheel FL and a right rear wheel RR thereof.Alternatively, one of the two chambers may be connected to two frontwheels FR and FL, and the other chamber may be connected to two rearwheels RR and RL. The reason why two chambers are formed independentlyas described above is for braking a vehicle even when one chamber fails.In the master cylinder 20, first and second oil pressure ports 24 a and24 b are formed to discharge the hydraulic pressure of the two chambers.

Further, a first spring 21 b is disposed between the first piston 21 aand the second piston 22 a of the master cylinder 20, and a secondspring 22 b is provided between ends of the second piston 22 a and themaster cylinder 20. That is, the first spring 21 b and the second spring22 b are respectively provided for the two chambers to store elasticforce due to the compression of the first piston 21 a and the secondpiston 22 a. The elastic force pushes the first and second pistons 21 aand 22 a to return to their original positions when the force pushingthe first piston 21 a is smaller than the elastic force.

Meanwhile, there is no gap between the master cylinder 20 and the inputrod 12 by pressing the input rod 12 for pressing the first piston 21 aof the master cylinder 20 against the first piston 21 a to be in contactwith each other. That is, when the brake pedal 10 is pressed, the mastercylinder 20 is directly pressed without apedal invalid stroke section.

The simulation device 50 for providing a reaction based on the pedaleffort of the brake pedal 10 is connected to a first backup path 251 tobe described below. According to the drawing, the simulation device 50includes a simulation chamber 51 which stores oil discharged from thefirst oil pressure port 24 a of the master cylinder 20, a reactionpiston 52 provided inside the simulation chamber 51, a pedal simulatorincluding a reaction spring 53 which elastically supports the reactionpiston 52, and a simulation valve 54 connected to a rear end of thesimulation chamber 51. Here, the simulation chamber 51 is installed tohave a displacement in a predetermined range determined by the oil whichflows into the simulation chamber 51 due to the reaction piston 52 andthe reaction spring 53.

The simulation valve 54 is formed to connect the rear end of thesimulation chamber 51 and the reservoir 30. That is, an inlet of thesimulation chamber 51 is connected to the master cylinder 20, the rearend of the simulation chamber 51 is connected to the simulation valve54, and the simulation valve 54 is connected to the reservoir 30, andthus, the pedal simulator, i.e., the entire inside volume of thesimulation chamber 51, is filled with oil.

The simulation valve 54 is formed with a solenoid valve in a normalclosed type which is in a closed state at ordinary time, and when adriver steps on the brake pedal 10, the simulation valve 54 is open totransfer brake oil to the simulation chamber 51.

Further, a simulation check valve 55 is installed parallel to thesimulation valve 54. The simulation check valve 55 allows oil to flowfrom the reservoir 30 into only the simulation chamber 51. That is, thereaction piston 52 of the pedal simulator compresses the reaction spring53, and oil inside the simulation chamber 51 is transferred to thereservoir 30 through the simulation valve 54. Thus, since the simulationchamber 51 is filled with oil, when the simulation device 50 operates,friction of the reaction piston 52 is minimized, and thus the durabilityof the simulation device 50 is improved, and the structure thereofblocks ingress of a foreign material from the outside.

Furthermore, when the pedal effort of the brake pedal 10 is released,supplying oil to the simulation chamber 51 through the simulation checkvalve 55 ensures that the pressure of the pedal simulator is quicklyreturned.

The electronic brake system according to the embodiment of the presentinvention includes a mechanically operating hydraulic pressure supplyunit 100 which receives an electrical signal from the pedal displacementsensor 11 for detecting a displacement of the brake pedal 10 when adriver steps on a brake, an oil pressure control unit 200 formed withfirst and second oil pressure circuits 201 and 202 each having twowheels which control the flow of the hydraulic pressure delivered to thewheel cylinder 40 provided on each wheel RR, RL, FR, and FL, a first cutvalve 261 which is provided on the first backup path 251 for connectingthe first oil pressure port 24 a and the first oil pressure circuit 201and controls a flow of the hydraulic pressure, a second cut valve 262which is provided on a second backup path 252 for connecting the secondoil pressure port 24 b and the second oil pressure circuit 202 andcontrols a flow of the hydraulic pressure, and an electronic controlunit (ECU) (not shown) which controls the hydraulic pressure supply unit100 and valves 54, 221, 222, 223, 224, 241, 242, 261, and 262 based onthe hydraulic pressure information and the pedal displacementinformation.

The hydraulic pressure supply unit 100 includes a pressure chamber 110in which a predetermined space is provided to receive and store oil, apressure piston 120 and an oil pressure spring 122 provided in thepressure chamber 110, a motor 140 which generates a rotatory power inresponse to the electrical signal of the pedal displacement sensor 11,and a power converter 130 which converts a rotary movement of the motor140 to a rectilinear movement to move the oil pressure piston 120 in astraight line. Here, the reservoir 30 and the pressure chamber 110 areconnected by an oil path 103 to supply the oil to the pressure chamber110. In addition, the signal detected by the pedal displacement sensor11 is transmitted to the ECU, and the ECU controls the motor 140 andvalves included in the electronic brake system according to theembodiment of the present invention which will be described below.Operations for controlling a plurality of valves due to a displacementof the brake pedal 10 will be described below.

As described above, the pressure chamber 110 is connected to thereservoir 30 by the oil path 103 and receives and stores the oil. Asdescribed above, the oil pressure piston 120 and the oil pressure spring122 which elastically supports the oil pressure piston 120 are providedin the pressure chamber 110. Here, the hydraulic pressure generated bythe pressure of the oil pressure piston 120 is transferred to the wheelcylinder 40 installed in each wheel RR, RL, FR, and FL through a mainoil pressure path 210.

The oil pressure piston 120 which presses the pressure chamber 110 isconnected to the power converter 130 which converts the rotatory powerof the motor 140 to a rectilinear movement in the pressure chamber 110and moves slidably.

The power converter 130 is a device which converts rotatory power torectilinear movement, and is formed with, for example, a ball screw nutassembly. For example, the power converter 130 may be formed with ascrew integrally formed with a rotating shaft of the motor 140 (notshown), and a ball nut which is screw-coupled with the screw withrestricted rotation and performs a rectilinear movement according to therotation of the screw. That is, the screw serves as the rotating shaftof the motor 140 and serves to perform a rectilinear movement of theball nut. Here, the oil pressure piston 120 is connected to the ball nutof the power converter 130 to press the pressure chamber 110 by therectilinear movement of the ball nut, and the oil pressure spring 122serves to return the oil pressure piston 120 to its original positionwhen the ball nut is returned to its original position.

Meanwhile, although not shown, the power converter 130 may also beformed with a ball nut rotatable by receiving rotatory power from therotating shaft of the motor 140 and a screw which is screw-coupled withthe ball nut with restricted rotation and performs a rectilinearmovement according to the rotation of the ball nut. Such ball screw nutassembly structure is a published well known technique for a devicewhich converts a rotary movement to a rectilinear movement, and thus adetailed description thereof will be omitted. Further, other than theball screw nut assembly, the power converter 130 according to theembodiment of the present invention should be understood to encompassany structure capable of converting a rotary movement to a rectilinearmovement.

The motor 140 is an electrical motor which generates a rotatory power inresponse to a signal output from the ECU and generates the rotatorypower in a normal or reverse direction depending on the ECU. Here, aprecise control is possible due to a control of a rotation angle orspeed of the motor 140. Such a motor 140 is a published well knowntechnique, and thus a detailed description thereof will be omitted.

Additionally, a check valve 102 is installed on the oil path 103 toprevent a backflow of the pressure of the pressure chamber 110. Thecheck valve 102 serves to prevent a backflow of the pressure of thepressure chamber 110 and also suctions and stores the oil in thepressure chamber 110 when the oil pressure piston 120 is reset.

When an electronic brake system including the above hydraulic pressuresupply unit 100 is used, the electronic brake system may be formed toprevent cases where the pressure in the pressure chamber 110 does notreturn to the atmospheric pressure in the process of suctioning oil intothe pressure chamber 110 while resetting the oil pressure piston 120.For example, a cut-off hole 111 is formed in the pressure chamber 110,and a connection path 101 which connects the cut-off hole 111 and theoil path 103 is formed between the pressure chamber 110 and the oil path103. Here, the cut-off hole 111 is formed at a position corresponding tothe initial position of the oil pressure piston 120. Thus, when the oilpressure piston 120 is reset, the oil pressure piston 120 isautomatically connected to the reservoir 30 through the connection path101, and thus the pressure of the pressure chamber 110 is returned toatmospheric pressure.

Meanwhile, a reference mark ‘PS1’ which is not described refers to afirst pressure sensor which detects a hydraulic pressure of the pressurechamber 110.

The oil pressure control unit 200 is formed with the first oil pressurecircuit 201 and the second oil pressure circuit 202 which receive ahydraulic pressure to each control two wheels. According to the drawing,the wheel controlled by the first oil pressure circuit 201 may be formedwith a right front wheel FR and a left rear wheel RL, and the wheelcontrolled by the second oil pressure circuit 202 may be formed with aleft front wheel FL and a right rear wheel RR. The wheel cylinder 40 isinstalled in each of the wheels FR, FL, RR, and RL and receives thehydraulic pressure to perform braking. That is, the oil pressure controlunit 200 receives the hydraulic pressure from the hydraulic pressuresupply unit 100 through the main oil pressure path 210 connected to thefirst and second oil pressure circuits 201 and 202, and each of the oilpressure circuit 201 and 202 includes a plurality of valves 221, 222,223, 224, 241, and 242 to control a flow of the hydraulic pressure.

The first oil pressure circuit 201 includes first and second inletvalves 221 and 222 connected to the main oil pressure path 210 tocontrol the hydraulic pressure transferred to the wheel cylinders 40 anda first balance valve 241 which connects or disconnects two wheelcylinders 40 respectively connected to the first inlet valve 221 and thesecond inlet valve 222. Specifically, the first inlet valve 221 isprovided on the first oil pressure path 211 which connects the main oilpressure path 210 and the right front wheel FR, and the second inletvalve 222 is provided on the second oil pressure path 212 which connectsthe main oil pressure path 210 and the left rear wheel RL. The firstbalance valve 241 is provided on a path which connects the first oilpressure path 211 and the second oil pressure path 212 and serves toconnect or disconnect the first and second oil pressure paths 211 and212 according to an opening or closing operation thereof.

The second oil pressure circuit 201 includes third and fourth inletvalves 223 and 224 connected to the main oil pressure path 210 tocontrol a hydraulic pressure transferred to the wheel cylinders 40 and asecond balance valve 242 which connects or disconnects two wheelcylinders 40 respectively connected to the third inlet valve 223 and thefourth inlet valve 224. Specifically, the third inlet valve 223 isprovided on the third oil pressure path 213 which connects the main oilpressure path 210 and the right rear wheel RR, and the fourth inletvalve 224 is provided on the fourth oil pressure path 214 which connectsthe main oil pressure path 210 and the left front wheel FL. The secondbalance valve 242 is provided on a path which connects the third oilpressure path 213 and the fourth oil pressure path 214 and serves toconnect or disconnect the third and fourth oil pressure paths 213 and214 according to an opening or closing operation thereof.

The opening and closing operations of the first to fourth inlet valves221, 222, 223, and 224 are independently controlled by the ECU and areperformed to transfer the hydraulic pressure generated from thehydraulic pressure supply unit 100 to wheel cylinders 40. That is, thefirst and second inlet valves 221 and 222 are formed to control thehydraulic pressure supplied to the first oil pressure circuit 201, andthe third and fourth inlet valves 223 and 224 are formed to control thehydraulic pressure supplied to the second oil pressure circuit 202.

According to one embodiment of the present invention, the hydraulicpressure may be transferred to each wheel cylinder 40 of the wheels FR,FL, RR, and RL by opening any two inlet valves of the four inlet valves221, 222, 223, and 224. For example, as shown in FIG. 2, the hydraulicpressure may be transferred to each wheel cylinder 40 of the wheel FR,FL, RR, and RL by opening the first inlet valve 221 of the first andsecond inlet valves 221 and 222 and opening the fourth inlet valve 224of the third and fourth inlet valves 223 and 224. That is, the hydraulicpressure passing through the first and fourth inlet valves 221 and 224is transferred to adjacent wheel cylinders 40 through the first andsecond balance valves 241 and 242. Here, although the hydraulic pressureis transferred to each wheel cylinder 40 by opening inlet valves 221 and224 respectively in the first oil pressure circuit 201 and the secondoil pressure circuit 202, the present invention is not limited thereto,and the hydraulic pressure may be transferred to each wheel cylinder 40by opening two inlet valves 221 and 222 provided in the first oilpressure circuit 201 according to the structure of the connection paths.Meanwhile, when there is a need for an emergency braking, the hydraulicpressure may also be quickly transferred to each wheel cylinder 40 byopening all of the inlet valves 221, 222, 223, and 224.

The first to fourth inlet valves 221, 222, 223, and 224 are providedwith solenoid valves in a normal closed type which operates a valve tobe open when an open signal is received in a state in which the valve isclosed at ordinary time. Further, the first and second balance valves241 and 242 are provided with solenoid valves in a normal open typewhich operates a valve to be closed when a close signal is received fromthe ECU in a state in which the valve is open at ordinary time.

According to one aspect of the present invention, when the electronicbrake system operates abnormally, the first and second backup paths 251and 252 are provided to directly supply oil generated from the mastercylinder 20 to each wheel cylinder 40. Specifically, the first cut valve261 is provided on the first backup path 251 to control a flow of theoil, and the second cut valve 262 is provided on the second backup path252 to control a flow of the oil. Further, the first backup path 251connects the first oil pressure port 24 a and the first oil pressurecircuit 201, and the second backup path 252 connects the second oilpressure port 25 b and the second oil pressure circuit 202. According tothe drawing, the first backup path 251 is connected to the first balancevalve 241 connected to the first oil pressure path 211 and the secondoil pressure path 212, and the second backup path 252 is connected tothe second balance valve 242 connected to the third oil pressure path213 and the fourth oil pressure path 214. Operating configurations ofthe first and second cut valves 261 and 262 will be described below.

The first and second cut valves 261 and 262 are provided with solenoidvalves in a normal open type which operates a valve to be closed when aclose signal is received from the ECU in a state in which the valve isopen at ordinary time.

Meanwhile, a reference mark ‘PS2’ which is not described refers to asecond pressure sensor which measures a pressure of oil of the mastercylinder 20.

Hereinafter, an operation of the electronic brake system according toone exemplary embodiment of the present invention will be described indetail.

FIG. 2 is an oil pressure circuit diagram when a brake of an electronicbrake system operates normally.

Referring to FIG. 2, when a driver starts braking, an amount of brakingrequired by the driver may be detected using pressure information andthe like via the pedal displacement sensor 11 responding to the brakepedal 10 pressed by the driver. The ECU (not shown) drives the motor 140by receiving an electrical signal output from the pedal displacementsensor 11. Further, the ECU may detect an amount of regenerative brakingvia a second pressure sensor PS2 provided at an outlet of the mastercylinder 20 and a first pressure sensor PS1 provided at the main oilpressure path 210 and may calculate an amount of frictional brakeaccording to a difference between the amount of braking required by thedriver and the amount of regenerative braking, and thus the size ofincrease or reduction of the pressure of the wheels may be determined.

Specifically, when a driver steps on the brake pedal 10 in an initialstage of braking, the motor 140 is operated, the rotatory power of themotor 140 is converted to a rectilinear movement by the power converter130 to move the oil pressure piston 120 forward, and a hydraulicpressure is generated by pressing the pressure chamber 110. Here, thefirst and second cut valves 261 and 262 installed on the first andsecond backup paths 251 and 252 respectively connected to the first andsecond oil pressure ports 24 a and 24 b of the master cylinder 20 areclosed so that an oil pressure generated from the master cylinder 20 isnot transferred to each wheel cylinder 40.

Further, the hydraulic pressure generated from the pressure chamber 110is transferred to the wheel cylinders 40 of the right front wheel FR andthe left front wheel FL by opening the first and fourth inlet valves 221and 224 so as to generate a braking force. At this point, the hydraulicpressure which flows through the first and fourth inlet valves 221 and224 is transferred to the wheel cylinders 40 of the left rear wheel RLand the right rear wheel RR through the first and second balance valves241 and 242 which are open. That is, the hydraulic pressure is suppliedto all of the wheel cylinders 40 by the opening operations of the twoinlet valves 221 and 224 selected from four inlet valves 221, 222, 223,and 224.

Such an operation is an operation in a typical braking situation, andwhen there is a need for an emergency braking, the hydraulic pressuremay also be quickly transferred to the wheel cylinders 40 by opening allof the inlet valves 221, 222, 223, and 224.

Meanwhile, the pressure generated by a pedal effort of the brake pedal10 pressing the master cylinder 20 is transferred to the simulationdevice 50 connected to the master cylinder 20. Here, the simulationvalve 54 in a normal closed type disposed at a rear end of thesimulation chamber 51 is open, and the oil filled in the simulationchamber 51 is transferred to the reservoir 30 through the simulationvalve 54. Further, the reaction piston 52 moves, and a pressurecorresponding to the weight of the reaction spring 53 which supports thereaction piston 52 is formed in the simulation chamber 51, and thus asuitable pedal sensitivity is provided to a driver.

Next, the case of a brake release when the electronic brake systemoperates normally will be described with reference to FIG. 3. As shownin FIG. 3, when a pedal effort on the brake pedal 10 is released,rotatory power is generated in a direction opposite to a forwarddirection in which the motor 140 moves the oil pressure piston 120, andthe oil pressure piston 120 is returned to an original position thereof.Here, the first to fourth inlet valves 221, 222, 223, and 224 and thefirst and second balance valves 241 and 242 are controlled by the sameopening and closing operations during braking. That is, the second andthird inlet valves 222 and 223 are provided in a closed state, and thefirst and fourth inlet valves 221 and 224 are open. Accordingly, thehydraulic pressure discharged from the wheel cylinders 40 of the firstoil pressure circuit 201 is transferred to the pressure chamber 110through the first balance valve 241 and the first inlet valve 221, andthe hydraulic pressure discharged from the wheel cylinders 40 of thesecond oil pressure circuit 202 is transferred to the pressure chamber110 through the second balance valve 242 and the fourth inlet valve 224.

In the simulation device 50, the oil inside the simulation chamber 51 istransferred to the master cylinder 20 due to the reaction piston 52returning to the original position by the reaction spring 53, and oil isfilled again in the simulation chamber 51 through the simulation valve54 and the simulation check valve 55 connected to the reservoir 30,thereby ensuring that the pressure of the pedal simulator is quicklyreset.

Meanwhile, when the oil pressure piston 120 moves due to the hydraulicpressure supply unit 100 of the above-described electronic brake system,a flow of the oil inside the pressure chamber 110 is controlled throughthe oil path 103 and the connection path 101 connected to the reservoir30.

Meanwhile, the electronic brake system according to one embodiment ofthe present invention may specifically control a control range bycontrolling the valves 221, 222, 223, 224, 241, and 242 provided in theoil pressure control unit 200 according to the pressure required by thewheel cylinder 40 each provided on wheels RR, RL, FR, and FL of two oilpressure circuits 201 and 202. For example, FIG. 4 illustrates the casein which braking is performed on only the corresponding wheel cylinderwhile operating an anti-lock brake system (ABS) and illustrates brakingonly a front wheel.

Referring to FIG. 4, the motor 140 operates according to a pedal effortof the brake pedal 10, rotatory power of the motor 140 is converted to arectilinear movement, and thus a hydraulic pressure is generated bymoving the pressure piston 120 forward and pressing the pressure chamber110. Here, the first and second cut valves 261 and 262 are closed andthe pressure of the oil generated from the master cylinder 20 is nottransferred to the wheel cylinder 40. Further, the second and thirdinlet valves 222 and 223 and the first and second balance valves 241 and242 are closed. Thus, the hydraulic pressure generated from the pressurechamber 110 is transferred to the wheel cylinder 40 of the right wheelFR through the first inlet valve 221 and is transferred to the wheelcylinder 40 of the left front wheel FL through the fourth inlet valve224. Accordingly, the hydraulic pressure is transferred to only thefront wheels FL and FR among the wheels RL, RR, FL, and FR.

According to one aspect of the present invention, since the operationsof the first to fourth inlet valves 221, 222, 223, and 224, and thefirst and second balance valves 241 and 242 are independently controlledas described above, the hydraulic pressure may be transferred to onlythe rear wheels RR and RL, or the hydraulic pressure may be transferredto the wheel cylinders 40 of the left front and the left rear wheels FLand RL, the right front and left rear wheels FR and RL, or whicheverrequires the oil pressure.

Further, in the electronic brake system according to the presentinvention, the brake pressure supplied to the wheel cylinder 40 may onlybe discharged by the corresponding wheel cylinder 40. For example, FIG.5 illustrates a case in which the electronic brake system operates in adump mode to only discharge the hydraulic pressure of the correspondingwheel cylinder 40, and illustrates dumping for only the rear wheels RRand RL.

Referring to FIG. 5, the motor 140 operates according to a pedal effortof the brake pedal 10, rotatory power of the motor 140 is converted to arectilinear movement, and thus a hydraulic pressure is suctioned intothe pressure chamber 110 by moving the oil pressure piston 120 backward.Here, the first and fourth inlet valves 221 and 224, and the first andsecond balance valves 241 and 242 are closed. Thus, the hydraulicpressure transferred to the wheel cylinder 40 of the right rear wheel RRand the wheel cylinder 40 of the left rear wheel RL is suctioned intothe pressure chamber 110 through the second and third oil pressure paths212 and 213 and the main oil pressure path 210. Accordingly, thehydraulic pressure is dumped to only the rear wheels RR and RL among thewheels RL, RR, FL, and FR and is transferred to the pressure chamber110.

According to one aspect of the present invention, since the operationsof the first to fourth inlet valves 221, 222, 223, and 224 and the firstand second balance valves 241 and 242 are independently controlled, thehydraulic pressure may be dumped to only the rear wheels RR and RL; orthe pressure of the corresponding wheel cylinders 40 of the left frontand left rear wheels FL and RL, the right front and left rear wheels FRand RL, or the like may be dumped by moving the oil pressure piston 120backward. Here, the pressure of the corresponding wheel cylinders 40 maybe dumped based on priorities if needed.

Finally, the case of abnormal operation of the electronic brake systemwill be described. Referring to FIG. 6, when the electronic brake systemoperates abnormally, each of the valves 54, 221, 222, 223, 224, 241,242, 261, and 262 is provided in an initial non-operational brakingstate. Thus, when a driver presses the brake pedal 10, the input rod 12connected to the brake pedal 10 moves leftward, and the first piston 21a in contact with the input rod 12 is simultaneously moved leftward.Further, the second piston 22 a is also moved leftward by the firstpiston 21 a. Here, since there is no gap between the input rod 12 andthe first piston 21 a, braking may be quickly performed. That is, thehydraulic pressure generated by pressing the master cylinder 20 istransferred to the wheel cylinders 40 through the first and secondbackup paths 251 and 252 connected for braking in a backup mode so as togenerate a braking force. Here, the first and second cut valves 261 and262 installed on the first and second backup paths 251 and 252, and thefirst and second balance valves 241 and 242 connected to the first andsecond backup paths 251 and 252 are formed with solenoid valves in anormal open type, and the simulation valve 54 and the first to fourthinlet valves 221, 222, 223, and 224 are formed with solenoid valves in anormal closed type, and thus the hydraulic pressure is immediatelytransferred to the wheel cylinders 40. Therefore, stable braking can beachieved, and the braking stability can be improved.

As is apparent from the above description, the electronic brake systemaccording to embodiments of the present invention may have the followingeffects.

First, the electronic brake system has an advantage of structuralsimplification from the conventional structures by minimizing the numberof valves for controlling a flow of oil pressure. Therefore, the size ofthe brake system, i.e., the size of a modulator block in which thevalves are installed, can be reduced allowing the electronic brakesystem to be implemented as a low cost product.

Second, since pressure is applied to all of the wheel cylinders usingonly two inlet valves among the four inlet valves for controlling a flowof a hydraulic pressure transferred to each wheel cylinder, operatingnoise and vibration of the valves can be minimized.

Third, since interlinked a motor and valves are controlled, theelectronic brake system can precisely control the pressure. In addition,the electronic brake system is formed with two oil pressure circuitseach connected to each of two wheels controlled independently and arelinked with and control a hydraulic pressure supply unit according tothe pressure required by each wheel and a determination by a prioritydetermining logic, thereby the control capability can be enhanced.

Fourth, when the brake system fails, a pedal effort of a driver isdirectly transferred to the master cylinder, so that braking the vehicleis still possible, and thus a stable braking force can be provided.

Although a few embodiments of the present invention have been shown anddescribed, it would be appreciated by those skilled in the art thatchanges may be made in these embodiments without departing from theprinciples and spirit of the invention, the scope of which is defined inthe claims and their equivalents.

Descriptions of reference numbers  10: brake pedal  11: pedaldisplacement sensor  20: master cylinder  30: reservoir  40: wheelcylinder  50: simulation device  54: simulation valve 100: hydraulicpressure supply unit 110: pressure chamber 120: oil pressure piston 130:power converter 140: motor 200: oil pressure control unit 201: first oilpressure circuit 202: second oil pressure circuit 210: main oil pressurepath 221: first inlet valve 222: second inlet valve 223: third inletvalve 224: fourth inlet valve 241: first balance valve 242: secondbalance valve 251: first backup path 252: second backup path 261: firstcut valve 262: second cut valve

What is claimed is:
 1. An electronic brake system including a reservoirin which oil is stored, a master cylinder having a first oil pressureport and a second oil pressure port and coupled with the reservoir toreceive the oil, a pedal displacement sensor configured to detect adisplacement of a brake pedal, and a simulation device connected to themaster cylinder and provided so that reaction is provided according to apedal effort of the brake pedal, the electronic brake system comprising:a hydraulic pressure supply unit configured to output an electricalsignal through the pedal displacement sensor to operate a motor when thebrake pedal operates, and configured to convert rotatory power of themotor to rectilinear movement; an oil pressure control unit having afirst oil pressure circuit and a second oil pressure circuit connectedto the hydraulic pressure supply unit through a main oil pressure path,and each configured to control two wheels so that a hydraulic pressureis received using a force generated by the hydraulic pressure supplyunit to perform braking; and an electronic control unit configured tocontrol the motor and valves based on hydraulic pressure information andpedal displacement information, wherein the oil pressure control unitincludes: a first inlet valve and a second inlet valve respectivelydisposed at upper streams of two wheel cylinders to control thehydraulic pressure flowing into the two wheel cylinders respectivelyinstalled on the two wheels provided in the first oil pressure circuit;a third inlet valve and a fourth inlet valve respectively disposed atupper streams of two wheel cylinders to control the hydraulic pressureflowing into the two wheel cylinders respectively installed on the twowheels provided in the second oil pressure circuit; a first balancevalve configured to connect or disconnect the two wheel cylinders towhich the first inlet valve and the second inlet valve are connected;and a second balance valve configured to connect or disconnect the twowheel cylinders to which the third inlet valve and the fourth inletvalve are connected, wherein the hydraulic pressure discharged from thefour wheel cylinders is controlled by a rotation in a direction oppositea rotation direction of the motor of the hydraulic pressure supply unitwhile braking.
 2. The electronic brake system of claim 1, wherein theinlet valves are provided with solenoid valves in a normal closed typewhich operates a valve to be open when an open signal is received in astate in which the valve is closed at ordinary time.
 3. The electronicbrake system of claim 1, wherein when the hydraulic pressure isdischarged from the wheel cylinders by rotating the motor of thehydraulic pressure supply unit in a reverse direction, the first inletvalve and the second inlet valve are open.
 4. The electronic brakesystem of claim 3, wherein when the hydraulic pressure is dischargedfrom the wheel cylinders by rotating the motor of the hydraulic pressuresupply unit in a reverse direction, only one of the first inlet valveand the second inlet valve is open and only one of the third inlet valveand the fourth inlet valve is open.
 5. The electronic brake system ofclaim 3, wherein the first and second balance valves are provided withsolenoid valves in a normal open type which operates a valve to beclosed when a close signal is received from the electronic control unitin a state in which the valve is open at ordinary time.
 6. Theelectronic brake system of claim 1, further comprising: a first backuppath configured to connect the first oil pressure port and the firstbalance valve so that oil is directly supplied to the wheel cylinderswhen the electronic brake system operates abnormally; a second backuppath configured to connect the second oil pressure port and the secondbalance valve; a first cut valve provided on the first backup path andconfigured to control a flow of the oil; and a second cut valve providedon the second backup path and configured to control a flow of the oil.7. The electronic brake system of claim 6, wherein the first and secondcut valves are provided with solenoid valves in a normal open type whichoperates a valve to be closed when a close signal is received from theelectronic control unit in a state in which the valve is open atordinary time.
 8. The electronic brake system of claim 1, wherein thehydraulic pressure supply unit includes: a motor configured to generatea rotatory power by the electrical signal of the pedal displacementsensor; a power converter configured to convert a rotary movement of themotor to a rectilinear movement; an oil pressure piston connected to thepower converter and configured to perform a rectilinear movement; apressure chamber slidably provided with the oil pressure piston andconnected to the first and second oil pressure circuits through the mainoil pressure path; and an oil pressure spring provided in the pressurechamber and configured to elastically support the oil pressure piston,wherein the pressure chamber is connected to the reservoir through anoil path to receive the oil.
 9. The electronic brake system of claim 8,wherein a check valve is installed on the oil path to prevent a flow ofa pressure of the pressure chamber backward, and to suction and storethe oil in the pressure chamber when the oil pressure piston isreturned.